When developing marginal offshore production fields it is important to keep the costs low. A substantial cost factor with known forms of development, is due to subsea pipelines and cables between christmas trees at the wells and product receiver sites, for example a platform or a floating production vessel. Typically the distances involved may be about 2 km. In this connection it is to be noted that modern drilling technology makes it possible to produce by means of a reduced number of christmas trees, because the boreholes or wells can have several branches. This will make it possible to develop subsea fields in some instances by employing a small number of wellheads and christmas trees assembled on a common subsea module or station at the seabed.
International patent application PC/NO96/00201 dated Jul. 8, 1996 relates to a system for offshore production of hydrocarbons by employing a moored production vessel or ship. The present invention can be regarded as a further development thereof and is based on the idea that the production vessel can by lying directly above or in the immediate vicinity of the subsea module in production at the seabed and that the well fluid flows are transferred directly between the module and the vessel without relying on pipelines or cables on the seabed. In this connection the invention is not exclusively based upon location of the production vessel by means of mooring, as according to the international patent application mentioned above, but can also employ mean as known per se for dynamic positioning of the vessel.